Question

Boyle's and Charles's laws become unreliable at high pressures and low temperatures. Why?

Answer 1

Boyle's law: When a gas is kept at constant temperature, its pressure is inversely proportional to its volume.

i.e. P ∝ 1 / V when T is constant.

Charle's law: When a gas is kept at constant pressure, the volume is directly proportional to the temperature.

i.e. V ∝ T when P is constant.

These two laws are valid when temperature and pressure are moderate to high. But at very high temperature, molecular interaction becomes very high and the gas will become a plasma, and again both Law will stop applying.

At high pressure (small volume), the gas particles are close to each other intermolecular force is very high. Intermolecular forces start to make the gas molecules adhere so they no longer behave as ideal gasses. Thus both gas laws are becoming unreliable.